/**
* a renderig form for representing the number on numberRay
*@author Bogdan Duca
*/
oa.rf.numberRay = new RenderingForm(
  "numberRay",
  "Render a binary addition or subtraction on the number ray",
  RenderingModeEL.individually
);
oa.rf.numberRay.isApplicableTo = function( apt){
  return (
      apt instanceof ArithmeticProblemType && 
      ( apt.numberType === NumberTypeEL.NonNegativeInteger ||
        apt.numberType === NumberTypeEL.Integer ) &&
      apt.operators.length === 1 &&
      ( apt.operators[0] === OperatorEL.plus ||
        apt.operators[0] === OperatorEL.minus ) 
  );
};